Conformational behavior of 3-borabicyclo[3.3.1]nonanes 1. Study of molecular dynamics in 3-methoxy-7 alpha-phenyl-1,5-dimethyl-3-borabicyclo[3.3.1]nonane

3-Methoxy-7 alpha-pheny1- 1,5-dimethyl-3-borabicyclo[3.3.1]nonane 5 in solu tion at room temperature exists in the double chair conformation, as shown by NMR studies. Increasing the temperature leads to an increase in the popu lation of the chair-boat conformation. At decreased temperature hindered ro tation around the B-O bond is observed for 5. Dissolving 5 in deuteropyridi ne leads to the reversible formation of complex 6, which exists in the chai r-boat conformation. The chair-boat conformation is also the most stable on e for chelate compound 7 with a tetracoordinated boron atom. (C) 1999 Elsev ier Science S.A. All rights reserved.